A significant by-product in the important commercial process of producing allyl chloride through the chlorination of propylene is 3,3-dichloropropene. Unfortunately, 3,3-dichloropropene and its homologs do not have a significant commercial use, so that the 3,3-dichloropropene produced in this manner has heretofore usually been incinerated.
As related in U.S. Pat. No. 5,072,063 to Langensee (hereafter, "Langensee"), a number of efforts have been made at the same time to produce the 1,3-dichloropropenes also produced as byproducts in the allyl chloride process, because of the known utility of both the cis- and trans- isomers of 1,3-dichloropropene as, for example, nematocides (German Patent Application No. 1,210,618), soil fumigants, insecticides and monomers in the production of plastics, resins and chemical intermediates.
These past efforts have included reacting 1,2-dichloropropane with a gas containing oxygen in the presence of a catalyst containing CuCl.sub.2, LiCl and ZnCl.sub.2 at 470 to 490 deg. Celsius, dehydrochlorination of 1,2,3-trichloropropane in the presence of oxygen or halogen, contacting 1,2-dichloropropane with chlorine to effect both chlorination and dechlorination reactions, or mixing 1,2-dichloropropane with allyl chloride and/or 1-chloropropene and reacting with chlorine at high temperature.
Langensee elected, in view of the availability and lack of utility of 3,3-dichloropropene and further citing the complicated, energy-consuming and/or inconvenient nature of the aforementioned processes, to pursue the isomerization of a 3,3-dihalopropene generally and 3,3-dichloropropene more particularly to the respective 1,3-dihalopropenes or 1,3-dichloropropenes and homologs thereof. This isomerization was accomplished by contacting the 3,3-dichloropropene with an alumina, silica or zeolite catalyst, and especially an alumina, silica or zeolite having acidic sites, in preferably a fixed bed, continuous process. In particular, Langensee contemplated the isomerization would be conducted directly on a 3,3-dichloropropene-containing, intermediate boiling byproduct stream from a distillation of the product stream from an allyl chloride process, to produce cis- and trans-1,3-dichloropropenes to be combined with the cis- and trans-1,3-dichloropropenes otherwise produced in the allyl chloride process and recovered through distillation.
An earlier Japanese patent, JP 80-69,523, was cited for also teaching an isomerization process, involving contacting 3,3-dichloropropene in the presence of hydrogen chloride with a catalytic amount of a zinc, iron, copper, tin, titanium or vanadium salt at between 0 degrees and 200 degrees Celsius. The difficulty found by Langensee with respect to the Japanese process, however, was that the catalyst was suspended in the reaction mixture and difficult to remove from the reaction mixture after completion of the rearrangement process.